Method of sizing paper



Patented Feb. 1, 1944 UNITED STATE s PATENT OFFICE Mn'rnon F s rzmo PAPER Chester 'L. Baker, Penn Wynne, and Charles H.

Dedrick, Drexel Hill, Pa., assignors to Philadelphia quartz Company, Philadelphia, Pa., a cor- 'poration oi Pennsylvania No Drawing.

6 Claims.

7 This invention relates to method of sizing paper; and it comprises a process wherein paper is sized by adding to the beater a sizing agent formed by aging an'alkali metal silicate in dilute solution, said solution being usually partially neutralized by the addition of an acid reagent and being aged until the point is reached at which Application June 28, 1939, Serial N0. 281,736

recirculated .it is occasionally possible to obtain a retention as high as 50 per cent.

We have discovered. a new method which makes use of a specially prepared silicate sizing agent and produces a retention of nearly 100 per cent of the $10: from the silicate of sodain the fin- ,the addition of aluminum sulfate to the solution in the beater produces a precipitate of hydrous silica in which the weight ratio of SiO: to A120: is at least about 8 to 1, the solution being then advantageously diluted in order to stabilize it prior to its addition to the beater, aluminum sulfate being also usually added to the beater in order to produce precipitation of said hydrous si1ica; all as more fully hereinafter set forth and as claimed.

In the conventional method of sizing paper with silicate of soda it is customary to first turnish the paper beater with water and fibrous maished sheet of paper- This effects an appreciable reduction in the amount of silicate of sodaand alum required to produce a' given degree of improvement in the finished sheet. Furthermore. our improved method requires less alum per hundred pounds of silicate of soda. In addition the sizing material retained in the sheet is nearly pure hydratedsilica as contrasted to thealuminum silicate retained in the conventional practice. A decided improvement in the quality of the paper is achieved, together with increased retention of the other sizing materials used. And other advantages are obtainedwhich will be set forth in detail below.

We havefound' that if a commercial silicate of soda solution is diluted with water, its alkali content being then partly neutralized with some acidic material, followed by allowing the solution to age for a, time, there is a rapid increase in the average statistical size of the colloidal siliceous aggregates inthe solution. This increase can be measured with the hydrogen electrode, which sulfate to form a flocculent precipitate. The pre-.

cipitate formed may or may not be a definite chemical compound, but as a rule the molecular shows a definite increase in pH with time. The increased size of the siliceousaggr'egates can also be demonstrated by precipitation with a polyvalent positiveion, such as AI The precipitate obtained becomes more siliceous as solutions ratio ofSlOz to A1203 is about 3:1 or less. A ratio,

of 3:1 would correspond to thechemical formula ,-Al2(SiO3) a. In this practice it is customary to usea silicate of soda having a S10: to Nazo weight ratio of from about 3.2 to 1 up to about 3.9 to 1. This material is used in ,theform of the concentrated commercial solutions containin from about 30 to 43 per cent solids. Usually about 30 to 50 pounds of hydrated aluminum sulfate is used for each100 pounds of commercial silicate of soda solution. I The degree of improvement in the sheet of'pa- .for longer periods of time.

of silicate of soda are used which have been aged Thus, it is'possible with a suitable dilution, partial neutralizing and aging of silicate of soda solutions to obtain a precipitate with aluminum sulfate which carries a high ratio of $102 to A120: and of course this'objective is attained with the use of a smaller quantity of aluminum sulfate. The A1203 from aluper obtained by the above procedure is generally roughly proportional to the amount of A120: plus $10: which is retained in the sheet. This retention iscustomarily evaluatedby determining the increase in ash content of the paper. In practising the conventional method one usually obtains minum sulfate is much more expensive than the S102 from silicate of soda, so that by the use of our invention it is possible to obtain the desired sizing effect at less cost.

,The rate of increase in the average statistical size of the siliceous aggregates, which occurs during the aging of our diluted and partly neutrala retention of about 30 per cent of the total A120: a

" and S10: added tothe beater as alum and silicate of soda. Inthose mills where the white water is able point. The optimum size of the siliceous asized silicate solution will depend upon the concentration of SiOz in the solution, the concentration of unneutralized alkali, the ambient temperature, etc. Whatever conditions are chosen, it is found that it is advantageous to arrest the size increase of the siliceous aggregates at a suit- It will be obvious from the "above that one can produce the desired state of siliceous aggregation over a fairly wide range of conditions and that the requisite aging time will vary considerably. For any given set of conditions it becomes necessary to determine the optimum aging time. This determination can be made .by

drawing oil samples of the solution at different time intervalsand using it in small laboratory paper sizing tests. It will be found that when cellulose fibers together so that a sheet of superior hardness and finish is obtained.

The chemical composition of the fiocculent precipitate formed by our method is quite unique in that it is composed almost entirely of hydrous silica. Analyses of paper sizedby our method show thatthe weight ratio of S: to A120: in the ash is usuallynot substantially below 8 to 1 and frequently this ratio reaches 44 to 1, corresponding to a silica content of 98per cent. It is probable that the precipitate formed in our proc.

. ess is really hydrous silica with a small amoun of adsorbed alumina.

We have found that the siliceous precipitate formed in the beater by our method seems to entrap. particulate matter which has been addedthe percentage retention of SiOzin the sheet is plotted against time of aging, a curve will be obtained whichindicates the best aging time for the partially neutralized silicate of soda solution.

In our work we have been able to obtain satisfactory results by using commercial silicate of soda solutions having a $102 to NaaO ratio falling within the range of 2.8:1 up to 3.9: 1. The range of concentrations to which these solutions may be diluted will fall between those containing 0.5 per cent SiOa and those containing 5.0 per cent SiOz.

It is advantageous to neutralize part of the alkali with an acid or an acid salt so that the partially neutralizedsilicateofsoda solution contains between 0.05 per cent and 0.20 per cent of NaaO as titrated with a standard acid using methyl orange as an indicator. or other chemical which is capable of reducing the alkalinity of the silicate solution within this range is applicable in our invention. For example, such salts as sodium bisulfate and alum can be employed or, if the presence of iron in the finished paper is unobjectionable, iron sulfate may be used. Any acid capable of neutralizing the silicate solution is applicable, for example CO1 can be used. These reagents serve to accel- .erate the aging procedure. The permissible temperature for the aging process may vary considerably, but we have obtained good results anyfor sizing purposes, such as clay, whiting, blanc y fix, titanium dioxide, and so forth, so that a" larger proportion of these materials are retained in the paper sheet than is ordinarily achieved in silicate-alum sizing, thus resulting in a sizable economy.

Our invention can be described somewhat more specifically by reference to the following specific Any acid, salt where within the range from about 5 C. to 40 C. 1

In carrying out our process in practice the properly conditioned silicate of soda solution is charged into the paper beater which has already been furnished with the necessary fiber and water. After the silicate solution has been thoroughly mixed with the other materials in the beater a small amount of alum is added. This results in the formation of a tough fiocculent precipitate of hydrous silica containing a small amount of adsorbed A1203. It is usually not necessary to add more than about 20 pounds of alum per 100 pounds of the original concentrated commercial silicate of soda solution, and good results can often be obtained with even smaller quantities. The best range is from about 5 to 30 pounds of alum to 100 pounds of the commercial silicate solution. And the silicate solution should be added in anamount ranging from about 10 to 100 pounds per 1000 pounds of paper stock, depending upon the extent of sizing desired. This results in a concentration of silicate in the beater ranging from about 0.005 to 0.4 per cent, based on the weight of the commercial silicate solution. The fiocculent siliceous precipitate is entrapped by the fibers during the paper making operation and, since it is partially dehydrated on the drier, it effectively cements the examples, which represent practical operations of our process. In each of these examples the results obtained are compared with those obtained in comparative tests in which conventional sizing methods were used.

'Emmple 1 For purposes-of comparison a lot of paper was sized with silicate of soda and alum according to the conventional procedure, as follows: 1000 pounds of bleached sulphite pulp was worked up in a beater and 40 pounds of a. liquid silicate of soda containing 8.85 per cent NazO and 28.7 per cent $102 was then added. Beating was continued for 15 minutes, whereupon 22 pounds of alum were. added. Beating was continued for another 15 minutes, following which the pulp was diluted with water and run on to the paper machine. Examination of the finished sheet showed that the treatment had increased the ash 0 by only 0.38 per cent, based on the weight of the paper. The increased ash analyzed 73 per cent S102 and 27 per cent A1203, which corresponds to a SiOzIAlzOa weight ratio of 2.7:1.00 and a retention of about 24.1 per cent of the $102 from the silicate of soda and about 30.5 the A1203 from the alum used.

Example 2 In another test we operated three beaters by adding to each 250 pounds dry weight of sulper cent of phite pulp, 750 pounds dry weight of ground wood,

poundsof clay and '8 pounds of rosin size,

water being added in proportion. Asizing agent within the present invention was made up by first mixing 40 pounds of a silicate of soda solution containing 8.85 per cent of NazO and 28.7 per cent of SiO: with 89 gallons of water at room temperatures. To this mixture we added 5 pounds of 66 B. sulfuric acid with vigorous agitation.

A sample of this partly neutralized silicate of soda solution was found to contain 0.075 per cent of NazO, as determined by titration against standard acid using methyl orange as an indicator.

This solution was allowed to-age for two hours at room temperature, which represents the optimum agingtime for this particular solution. It was then diluted to 250 gallons with water to stabilize it and to preserve the optimum statistical, size in the colloidal iliceous aggregate present. This quantity of sizing agent was added to each'beater in addition to 10 pounds of alum.

2,s4o,72s I e were used to 1000 pounds of uplp. The results The properties of the flnished sheet obtained in this test were then determined and compared with those of a sheet Obtained in a comparative test in which the same materials were furnished to the beaters and in the same quantities with the single exception that our special sizing agent was omitted. The character of the two sheets produced in these tests is shown in Table I.

* Conventional Ournew Tim I 1.000 pounds pulp method method Results '0! comparative tests 1 a 0.12 0.0a I Sizedb Sledb co ven it? 0111' l y I1 chwterifsmt I meoilxi 'tlonal method 0.1a 0.00 V 0.1a an l ds 34% 35% i 8'8 a l1 18mg t fi 8.5 s 8.4 0.14 0.88 47 40 0.15 0.88 11 57 0.15 o.as 0.0a; 0.036 0.18 use 5.33 4.23 I l Clagpnd ilber remalningin 20 If the results in Table'II are compared with fiol fi'ffi f.f iifff f. I mar/1,000 gal. "am 1,000 gal. .rgi se Obtained in the conventional method test described ln-Example 1 it will be seen that it The values in the above table for the sugardye size test were determined by following the procedure outlined on page 714 of the 'Iechnoe logic Paper of theBureau of Standards, No. 326, while the values for the formation were determined-by using the Gurley densometer as'described in Paper Testing Methods under the heading Air Resistance or Porosity, published for the- Technical Association of thePulp and Paper Industry by the Lockwood Trade Journal Co., lOEast 39th St.,-' New York city (1928), pages 73 to 76. The percentretention values given in the table represent the percentage of $102 plus A120: plus clay retained by the. paper, in terms of the total quantities of these substances added to the beater. The quantities retained by the paper were obtained by ash determinations.

Table I shows clearly the important advantages which are derived from following the present invention. For example, the resistance of the sheet to penetration by a sugar dye solution has been substantially increased which is doubtless due to the higher retention of the rosin size in the process of the present invention. The formation of the sheet produced by our method is considerably better as is also the percentage of ash and the apparent clay retention. 01 particular importance is the fact thatwthe white water from the suction box contained less clay and short fibers when our method was used. This shows clearly that a higher retention of short v Test: 11 I Per cent ash increase in paper during sizing v Pounds alum used per requires about 22 pounds of alum in the 'conventional method to produce an ash retention of 0.38 per centwhereas this retention can be. ob-

tained by our new method by the use of a quantity of alum somewhere between 3. and 4 pounds.

In other words'approximately 80 per cent of the alum employed in the conventional method can be saved by the use ofthe new. method. The table also shows that the use of 7 pounds of alum in the new method will produce approximately twice the ash retention obtained by the use of 22 pounds in the conventional method. In other words the sizing effect can be doubled and at the same time a saving of about 70 per cent in alum,

be the best embodimentsof our process, it is evident that the specific procedures described can be varied to a considerable extent \vithout' departing from the purview of this invention. It is possible to employ solutions of potassium silicats or the silicates of other alkali metals in place of sodium silicate solutions. Our sizing agent may be added to the paper stock at any convenient place in the paper manufacturing procedure provided that suflicient time is provided for the siliceous precipitate to form and to combine with the paper stock in order to produce the desired sizing. The present invention can be employed in connection with-any of the customary paper manufacturing processes. It is only necessary to substitute the sizing agent of the present invention in whole or in part for the different amounts of added alum by the use of our process, in comparison'with the conventional process wherein silicate of soda. and alum are used as sizing agents. In making these tests the same quantities of silicate of soda were added as sizing agents but in the tests representing our new process the silicate of soda had been aged.

to approximately the optimum extent by dilusizing agent or agents employed previously. Our sizin agent, can, of course, be employed in adtion which fall within the scope of the following claims will be immediately evident to. those skilled in this art.

What weclaim is: r I

v 1. In the sizing of papenthev process which comprises forming a dilute solution of sodium within the range of about 2.821 to 3,9:1 and a concentration within the range of about 0.5 to 5.0 per cent by weight of S102, reducing the alkalinity-of the solution until it is within the range of about 0.05 to 0.2 per cent NazO as determined by titration using. methyl orange as i dicator, aging the resulting solution until the addition of a'small quantity of aluminum sulfate causes the precipitation of a hydrous silicate having a weight ratio of S102 to A120: not substantially less than 8 to 1, adding the aged solution to a beater furnished with the usual water and paper pulp and also adding suflicient aluminum weight, adding an neutralizing reagent to produce an alkalinity ranging from about 0.05 to 0.2 per cent NazO, aging the resulting solution until, upon the addition of a small quantity of alum, a precipitate of hydrous silica will form havinga weight ratio of $102 to A1203 of not substantiallyless'than 8 to l. and diluting the aged solution substantially to stabilize it.

3. In the process of sizing paper wherein sizing agents are added to a beater furnished with the usual.dilute paperstock, the steps'which comprisediluting a concentrated commercial silicate of soda solution having a weight ratio of SiOato NaOa within the range of about 2.8:1 to 3.9:1 to produce a concentration within the range of I about 0.5 to 5.0 per cent by weight OfSiOz, re-.

ducing the alkalinity of said solution to within 2,340,725 silicate having 'a w ight ratio of $102 to NazO the range tr about 0.05 to 0.2 per cent NaOz: as

determined by titration with methyl orange as" indicator, aging the resulting solution to the point at which, when added to said stock in con- Junction with aluminum sulfate in quantities suflicient to produce the desired degree ofsizing a precipitate of hydrous silica is formed in which the weight ratio of S102 to Ali-Oz is at least about 8 to 1, then adding the so-prepared solution to the beater in sizing. concentrations and precipitating said hydrous silica in the presence of aid paper stock, thereby causing saidprecipitate to combine withthe paper stock.

4. The process of claim 3 wherein the hydrous" silica precipitate is formed by the addition of aluminum sulfate to the beater in .the proportion of about 5 to 30 pounds to 100 pounds of the con-f centrated commercial silicate of soda solution.

5. The process of claim 3 wherein the silicate is used in an amount ranging from about 10 to 100 pounds ofthe concentrated commercial solution to 1000 pounds of paper stock.

6. In the processof sizing'paper wherein sizing agents are added to a beater furnished with the usual dilute paper stock, the steps which comprise diluting a silicate of soda solution containing about 8.85 per cent of New and 28.7 per cent reduce the alkalinity to about 0.075 per cent NazO, as determined by titration with methyl orange as indicatonaging the resulting solution for a period of about 2'hours, diluting the aged solution with water and adding it to the beater 1 together with suiiicient aluminum sulfate to cause the precipitation of hydrous silica, thereby causing said stock. I

I CHESTER L. BAKER.

' CHARLES H. DEDRICK.

precipitate to combine with the paper 

